Mechanical welding press

ABSTRACT

A mechanical press has an elevated welding station and a workpiece conveyor extending through the press at a level spaced below the welding station. A lift mechanism below the conveyor is designed to elevate the platen with a straight line vertical motion in two successive steps to first engage a workpiece on the conveyor and then elevate the workpiece to the welding station. Thereafter the lift mechanism lowers the platen with a straight line vertical motion in two successive steps to first deposit the welded workpiece on the conveyor and then recede to its starting position. The drive for the lift mechanism gradually accelerates the platen at the beginning of each step and gradually decelerates it to a near zero velocity at the end of each step.

This invention relates to a mechanical welding press particularly of thetype wherein workpieces are delivered to and from the press by means ofa conveyor.

In one form of welding press a workpiece or an assembly of severalworkpieces is lifted by a lift mechanism to an elevated work station inthe press where the workpieces are contacted by welding guns to makeseveral spot welds thereon. The lift mechanism is then actuated to lowerthe welded assembly. In some welding presses of this type the workpiecesare conveyed into and out of the press by a conveyor. With such pressesthe lift mechanism must first elevate to a position wherein it engagesthe conveyor-supported workpieces and then lifts the workpieces to theelevated welding station. After the welding operation is completed thelift mechanism must reverse its operation to first lower the weldedassembly onto the conveyor and then retract to its lowermost startingposition.

As a practical matter the lift mechanism should be relatively compactsince it is most desirably located beneath the conveyor. In addition, itshould be structurally very rigid, both laterally and vertically, in thecase of a welding press, to resist the pressure of numerous weldingguns. Furthermore, it should be capable of raising and lowering theworkpieces in an accurate vertical path and without jarring them out ofalignment with respect to the welding guns.

The primary object of the present invention is to provide a weldingpress with a structurally highly rigid lift mechanism which occupies arelatively small amount of space in relation to its vertical stroke andwhich is designed to raise and lower a workpiece between a conveyor andan elevated welding station in a vertical straight path.

A further object of this invention is to provide a lift mechanism in apress of the type described that is designed to accelerate from a restposition to a relatively high velocity and then decrease to a near zerovelocity at the end of each multiple stage stroke so that it gentlyengages a workpiece on the conveyor and lifts it to the elevated weldingstation and thereafter gently deposits the welded assembly back onto theconveyor.

These and other objects, features and advantages of the presentinvention will become apparent from the following description andaccompanying drawings, in which:

FIGS. 1, 2, 3 and 4 show in a diagrammatic way the operation of awelding press and conveyor and a workpiece lifting and loweringmechanism;

FIG. 5 is a fragmentary longitudinal sectional view of a lift mechanismaccording to the present invention shown in the fully raised position;

FIG. 6 is a view similar to FIG. 5 and showing the lift mechanism in thefully lowered position;

FIG. 7 is a view similar to FIG. 5 and showing the lift mechanism in theintermediate dwell position;

FIG. 8 is an end view of the lift mechanism as viewed along the lines8--8 in FIG. 5;

FIG. 9 is a fragmentary elevational view of the lift mechanism at thedrive end thereof;

FIG. 10 is a sectional view along the line 10--10 in FIG. 9; and

FIG. 11 is a sectional view along the line 11--11 in FIG. 9.

Referring first to FIGS. 1 thru 4, there is illustrated a welding press10 through which workpieces 12 are conveyed one at a time by a conveyor14. A platen or work support 16 below conveyor 14 is designed to beelevated so as to engage the workpiece 12 within the press and elevateit to a position where it is contacted by the guns 18 of a mechanicalwelding press assembly 20 where several spot welds will be made. In FIG.1 a workpiece 12 is shown located on the conveyor vertically alignedwith the welding assembly 20 and the platen 16. In FIG. 2 platen 16 isshown raised so as to engage the workpiece 12 on the conveyor. FIG. 3shows the platen 16 raised to its uppermost position wherein theworkpiece 12 is contacted by the welding guns 20 to effect the spotwelds. Thereafter, as shown in FIG. 4, platen 16 is lowered to depositthe welded workpiece back onto the conveyor. The platen is then loweredto the position shown in FIG. 1 and the conveyor 14 is indexed toposition the next successive workpiece 12 into the press and dischargethe welded assembly so that the cycle can be repeated.

The platen 16 is illustrated as a work supporting plate 22 reinforced bya depending skirt 24 and having a pair of depending brackets 26 on theunderside thereof. The lift mechanism for the platen is generallydesignated 28 and includes a base 30 on which two pair of substantiallyidentical linkages 32,32' are arranged. As shown in FIG. 8 each linkageincludes a torque tube 34 journalled for rotation on base 30 by means ofbearings 36 and shafts 38. On each torque tube 34 there is fixedlymounted a pair of axially spaced parallel levers 40. A pair of axiallyspaced bellcranks 42 are pivotally connected to the free end of eachlever 40 by the hinge pins 44. The depending brackets 26 on theunderside of platen 16 are pivotally connected to each pair ofbellcranks 42 as by the hinge pins 46. At the third corner of each pairof bellcranks there is mounted, as by a shaft 48, a guide roller 50 thatis guided in a rectilinear path by a guide track 52 fixedly mounted oneat each side of base 30. The four bellcranks 42 in each linkagearrangement 32,32' are interconnected for movement in unison by atorsion tube 54.

It will be appreciated that the arrangement of links 40,42 and thetorque tubes 34,54 provides a lift mechanism that possesses a highdegree of lateral stiffness. The two sets of linkages can be tiedtogether by the two torque tubes since the links in each set do notcross over one another. This eliminates the need for vertical sideguides for platen 16 which are costly and difficult to maintain inaccurate alignment. In addition, the absence of side guides enables thepress to accommodate larger panels than would otherwise be the case forthe same size press.

As shown in FIG. 9, the lift mechanism is preferably powered by areversible electric motor 56 through a gear box 58. Referring to FIG.11, the output shaft 60 of gear box 58 has a crank 62 mounted thereon onwhich is fixed a gear 64. A gear rack 66 meshes with gear 64 and isretained in engagement therewith by a bracket 68 that is journalled onthe axis of gear 64 by a shaft 70. The pitch line of the teeth of gear64 passes through the axis of output shaft 60. This arrangement is amotion generating device of the type disclosed in U.S. Pat. No.3,789,676 which in response to rotation of output shaft 60 imparts acycloidal motion to gear rack 66. In the position shown in FIG. 11 aslight angular displacement of shaft 60 causes little or no lineardisplacement of rack 66. As shaft 60 rotates through one revolutionthere will be a gradual acceleration of rack 66 until the maximumvelocity is reached where the rack is driven by the teeth of gear 64that are spaced a maximum distance from the axis of shaft 66. Thisoccurs after shaft 60 has rotated through one-half revolution.Thereafter, rack 66 will gradually decelerate and its velocity willapproach or become zero at one complete revolution of output shaft 60.

One end of rack 66 is pivotally connected as at 72 to a lever 74 fixedto a shaft 76 that is journalled between brackets 78 on the base 80 ofthe drive mechanism. A second lever 82 on shaft 76 is pivotallyconnected as at 84 to one end of a generally horizontally extending link86. The other end of link 86 is pivotally connected as at 88 with alever 90 fixed to tube 34'. Another link 92 has one end connected tolever 90 as at 94 and its opposite end pivotally connected as at 96 to alever 98 on tube 34. In the preferred arrangement equal angulardisplacements are imparted to tubes 34 and 34' in response to generallyhorizontal displacement of link 86.

Although the above described cycloidal drive is preferred for poweringthe lift linkage for the platen, other non-cycloidal prime movers may beutilized. This is especially true if there is no necessity to deceleratethe platen at the end of its successive motions. Examples of otherusable prime movers include cranks, lead screws, cylinders, etc.

The linkages 32 and 32' are of the type disclosed in U.S. patentapplication Ser. No. 06/399,465, filed Oct. 19, 1982 by John HenryBrems, one of the co-inventors named herein. The linkage arrangement isdesigned to produce a straight line movement of the hinge pins 46,46'which interconnect the linkages with platen 16. As explained in theaforesaid application, in order to obtain such straight line motionspecific design parameters of the linkages must be adherred to. Thedistance between the axis of pin 44 and the axis of rotation of tube 34,the distance between the axes of pins 44 and 46 and the distance betweenthe axes of pin 44 and guide roller 50 must all be equal. In addition,the path of travel of guide roller 50 must be a straight line passingthrough the axis of rotation of tube 34. Furthermore, if a line drawnthrough the axes of roller 50 and pin 46 is horizontal when the axes ofroller 50, pin 44 and tube 34 are colinear, then the path of movement ofpin 46 will be vertical. This condition is shown in broken lines in FIG.5 wherein the axis of tube 34 is designated P₁, the axis of pin 44 isdesignated P₂, the axis of guide roller 50 is designated G and the axisof pin 46 is designated O. When lever 40 is rotated counterclockwisefrom the solid line position to a position wherein the axes P₁, P₂ and Gare colinear, the line A-B between the axes G and O is horizontal andthe line C-D between the axes O and P₁ is a vertical straight line whichcorresponds to the path of travel of hinge pin 46.

It will be observed that the broken line position shown in FIG. 5 is anintermediate position. The solid line position of the linkage shown inFIG. 5 represents the fully raised position of platen 16 and correspondsto the position of the drive linkage shown in FIG. 9. After onerevolution of the output shaft 60 of gear box 58 in a counterclockwisedirection the linkage will assume the position shown in FIG. 7 whereinthe platen 16 is lowered approximately one-half its full stroke and theworkpiece 12 on the platen will be deposited gently at near zerovelocity on the conveyor 14. After another full revolution of the outputshaft 60, the platen 16 will be lowered to the fully retracted positionshown in FIG. 6 which is substantially below the conveyor 14. At thistime the conveyor can be operated to advance the welded assembly out ofthe press and to advance another panel into the press to a positiondirectly above platen 16.

If the distances between the corresponding pivot axes in the two sets oflinkages 32,32' are of exactly the same length and the inclination ofthe two guide tracks 52 and 52' are at the same angle, plate 16 willassume a horizontal position at all times. While such an arrangement ispreferred in most instances, nevertheless, depending upon theconfiguration of the workpiece and the manner in which it is to be spotwelded, it may be desirable to cause the plate 16 to assume a horizontalposition when it engages a workpiece on the platen and to assume asomewhat inclined position when the workpiece is engaged by the guns 18of the welding assembly 20. It will be apparent that, if the links inthe linkage 32 are shorter than the corresponding links in the linkage32', hinge pins 46 will be displaced vertically through a shorter strokethan hinge pins 46'. Likewise, if the links in the two sets of linkagesare of the same size but the guide tracks 52 are inclined to thehorizontal at a greater angle than the guide tracks 52', hinge pins 46will be displaced vertically through a shorter stroke than hinge pins46'. The vertical stroke of hinge pins 46 can also be increased ordecreased in relation to the vertical stroke of hinge pins 46' bycausing levers 90,98 to rotate through different arcuate extents duringeach of the multiple strokes of link 86. It will therefore be apparentthat, although two hinge pins 46,46' are constrained to move alongvertical axes, the linkages can be so designed as to cause the platen 16to assume an inclined position throughout its vertical travel or at apredetermined location in its stroke.

The invention has been shown and described as a welding press. It isobvious that the press could be designed for other than a weldingoperation. This invention is applicable to various types of presseswhich require a workpiece to be raised from a conveyor to elevatedtooling on the press. Thus, the press could be employed for sealingapplications, trimming, piercing, routing or a variety of otheroperations customarily performed on panels and other workpieces.

We claim:
 1. In a machine having a conveyor extending therethrough and awork station located vertically above a portion of the conveyor withinthe machine, the combination of:A. a vertically movable workpiecesupport in the machine; B. a lift mechanism located below the conveyorand connected with the support for lifting a workpiece from the conveyorin a substantially straight vertical path to said work station andsubsequently lowering the workpiece in a reverse vertical path from thework station onto the conveyor, said lift mechanism comprising:1. abase,
 2. a first pair and a second pair of links longitudinally spacedapart, means rigidly connecting together the links of each pair inaxially spaced apart relation, each link having a first pivot pointconnecting each link to said base and a second pivot point displacedfrom said first pivot point by a first distance,
 3. a first pair and asecond pair of bell cranks longitudinally spaced apart, means rigidlyconnecting together the bell cranks of each pair in axially spaced apartrelation, each bell crank connected with one associated link, each bellcrank having three triangularly related pivot points thereoncomprising:(a) a center pivot point connected with its respective linkat said second pivot point, (b) a guide pivot point spaced from saidcenter pivot point by a second distance, and (c) an output pivot pointspaced from said center pivot point by a third distance and connectedwith said support, said pivot points permitting relative pivotalmovement of the links and bell cranks about generally horizontallyextending parallel axes, the triangles defined by the three pivot pointson the bell cranks of each pair being similar triangles, the distanceson each of the connected links and bell cranks of each pair between thefirst and second pivot points, between the second and guide pivot pointsand between the second and output pivot points being substantiallyequal,
 4. a first pair and a second pair of guides longitudinally spacedapart on said base for guiding each associated guide pivot point along astraight line passing through the pivot axis of the first pivot pointand inclined to the horizontal at an angle such that when each link ispivoted to a position wherein the first, second and guide pivot pointslie in said straight line, a line extending between said first pivotpoint and said output pivot point is substantially perpendicular to thehorizontal; and
 5. drive means for pivoting said first and second pairsof links in unison and alternately in opposite angular directions. 2.The combination called for in claim 1 wherein the spacing between thecorresponding pivot points on the two links and bellcranks of both thefirst and second pair are substantially equal.
 3. The combination calledfor in claim 1 wherein the pivot guides of both the first and secondpair are inclined to the horizontal at substantially the same angle. 4.The combination called for in claim 3 wherein all of the guides aresubstantially parallel to each other.
 5. The combination called for inclaim 4 wherein all of the links are rotated in the same directions. 6.The combination called for in claim 1 wherein said means for rotatingthe links are designed to pivot the links through two successive stepsof equal extent, first in one direction and then in the oppositedirection, with an accelerating-decelerating motion at the beginning andend of each step, the extent of pivotal motion of each link during eachstep being determined such that the support is located below theconveyor at the beginning of the first step and at the end of the fourthstep at a level closely approaching or contacting a workpiece on theconveyor at the end of the first step and at a level wherein theworkpiece is disposed at said work station at the end of the secondstep.
 7. The combination called for in claim 6 wherein the two links ofeach pair are rotated through the same arcuate extent in each step. 8.The combination called for in claim 6 wherein said workpiece supportextends horizontally, the spacing between the corresponding pivot pointson all the links and bellcranks are exactly equal, all the links andbellcranks have exactly the same orientation, all the guides areparallel and all the links are pivoted through the same arcuate extentand in the same direction during each step.
 9. The combination calledfor in claim 1 wherein said work station comprises a welding pressassembly.
 10. The combination called for in claim 1 wherein said meansfor pivoting the links produces a near zero velocity at the end of eachsuccessive step.
 11. The combination called for in claim 1 wherein thelinks of each pair are rigidly connected together by a torgue tubeextending between them and the bell cranks of each pair are rigidlyconnected together by a torque tube extending between them.
 12. In amachine having a conveyor extending therethrough and a work stationlocated vertically above a portion of the conveyor within the machine,the combination of:A. a vertically movable workpiece support in themachine; B. a lift mechanism located below the conveyor and connectedwith the support for lifting a workpiece from the conveyor in asubstantially straight vertical path to said work station andsubsequently lowering the workpiece in a reverse vertical path from thework station onto the conveyor, said lift mechanism comprising:1. abase,
 2. at least one first link and at least one second linklongitudinally spaced apart, each link having a first pivot pointconnecting each link to said base and a second pivot point displacedfrom said first pivot point by a first distance,3. at least one firstbell crank and at least one second bell crank longitudinally spacedapart, each bell crank connected with one associated link, each bellcrank having three triangularly related pivot points thereoncomprising:(a) a center pivot point connected with its respective linkat said second pivot point, (b) a guide pivot point spaced from saidcenter pivot point by a second distance, and (c) an output pivot pointspaced from said center pivot point by a third distance and connectedwith said support, said pivot points permitting relative pivotalmovement of the links and bell cranks about generally horizontallyextending parallel axes, the triangles defined by the three pivot pointson all of the first bell cranks and all of the second bell cranks beingsimilar triangles, the distances on each of the connected links andassociated bell cranks between the first and second pivot points,between the second and guide pivot points and between the second andoutput pivot points being substantially equal,4. at least one firstguide and at least one second guide longitudinally spaced apart on saidbase for guiding each associated guide pivot point along a straight linepassing through the pivot axis of the first pivot point and inclined tothe horizontal at an angle such that when each link is pivoted to aposition wherein the first, second and guide pivot points lie in saidstraight line, a line extending between said first pivot point and saidoutput pivot point is substantially perpendicular to the horizontal; and5. drive means for pivoting all of said first and second links in unisonand alternately in opposite angular directions.